For an increase in power, and for resource-conserving and environmentally friendly operation of internal combustion engines, use has long been made of exhaust-gas turbochargers which permit pre-compression of the air taken in by the internal combustion engine. Normally, such exhaust-gas turbochargers have, in the exhaust-gas flow of the internal combustion engine, a turbine which is connected by means of a shaft to a compressor impeller in the intake duct.
Efficient operation of the turbine on the exhaust-gas side requires different settings of the gas guidance in the turbine under changing operating conditions of the internal combustion engine. Wastegate valves, for example, are known for this purpose.
In the case of diesel engines, but increasingly also in the case of Otto-cycle engines, use is furthermore often made of adjustable turbine geometries. These provide adjustable guide vanes which are arranged upstream of the turbine impeller. The guide vanes are arranged in a movable and adjustable manner and within a ring-shaped gap around the turbine.
Since, with changing operating conditions, it is the case in particular that the temperature of the exhaust-gas flow changes, the guide vanes are also subject to thermal changes, in particular thermal contraction and expansion in the event of temperature changes. This gives rise to particular problems in conjunction with the fact that, in the case of reduced dimensions of the guide vanes, gaps form in relation to the walls of the ring-shaped gap, as a result of which the efficiency of the turbine as a whole is decreased.
The detrimental effect of such gaps or of an inadequately defined ring-shaped gap geometry has already been recognized, and is the subject of the US patent application US 2012/0243973 A1. Said document describes guide vanes which are mounted on a holding ring so as to be pivotable about a pivot axis and which are each connected to actuation levers. The actuation levers are pivotable and are preloaded in a direction parallel to the pivot axis by an oblique actuation surface in order to compensate any existing mechanical play and in order to realize defined positions of the guide vanes.